Interface apparatus and method, and image output apparatus having interface apparatus

ABSTRACT

An interface apparatus capable of appropriate connection with external devices having various specifications. Control signal DRVSEL is used for setting output method of a signal from output circuit  801  to an open-collector drive or a totem-pole drive. 3-State buffer  904  which drives a communication path comes into high-impedance status when its enable input is at a H level, on the other hand, when the enable input is at a L level, drives its output with the same logic as that of AND gate output. When the signal DRVSEL is at the L level, the 3-state buffer  904  drives the output only when its internal signal is at the L level, thus output is made in the open-collector drive. On the other hand, when the signal DRVSEL is at the H level, the 3-state buffer  904  drives the output with the same logic as that of its internal signal, thus output is made in the totem-pole drive.

This application is a division of application Ser. No. 08/755,369 filedon Nov. 25, 1996 U.S. Pat. No. 6,212,583.

BACKGROUND OF THE INVENTION

This invention relates to an interface apparatus and method and an imageoutput apparatus having the interface apparatus and, more particularlyto an interface apparatus for transmitting/receiving information with anexternal apparatus via a communication line, a method for negotiatingfor transmitting/receiving information between apparatuses, and an imageoutput apparatus having the interface apparatus.

Generally, a printer and an information processing device are connectedvia a fixed type communication interface. In each device, anopen-collector type interface circuit or totem-pole type interfacecircuit is fixedly provided, and it is impossible to select an interfacecircuit in accordance with the specification of communicationdestination device.

However, in a case where a device has only an open-collector typeinterface circuit, even if another device as a communication destinationuses a totem-pole type interface, high-speed communication cannot beperformed. In an open-collector type interface circuit, a transitionalperiod where a signal level changes from a high level to a low level,and a transitional period where the signal level changes from the lowlevel to a high level are greatly different. Especially, the transitionof signal level from the low level to the high level is made veryslowly.

In a case where the device has only a totem-pole type interface circuit,if the power of the communication destination device is turned off andthe communication line is in short-circuit or in low-impedance status,overcurrent occurs, which consumes a large amount of electricity and maycause the interface circuit to generate heat.

There is a tendency of signal voltage swing to be complicated, sincesmall signal voltage swing is used to increase communication speed or tosave electricity. A device corresponding to only one signal voltageswing cannot handle communication with devices of variousspecifications. In many cases, the input characteristics of signals andthe output characteristics of signals do not coincide with each other.

Further, even though the device can communicate with a high-performancedevice, if the device cannot communicate with existing devices, itcannot be efficiently utilized. For example, it is inconvenient thatevery time a new device is introduced, all the devices to be connectedto the new device must be changed.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the aboveproblems, and has its object to provide an electronic device which canbe appropriately connected to external devices having variousspecifications.

According to the present invention, the foregoing object is attained byproviding an interface apparatus for transmitting and receivinginformation with an external device via a communication path,comprising: acquisition means for acquiring selection informationsupplied from the external device via the communication path; and drivemeans for selecting one of a plurality of drive methods based on theselection information acquired by the acquisition means and driving thecommunication path.

Preferably, in the interface apparatus, the plurality of drive methodsincludes a first drive method for driving the communication path in anopen-collector drive and a second drive method for driving thecommunication path in a totem-pole drive.

Preferably, in the interface apparatus, the plurality of drive methodsincludes a plurality of drive methods for driving the communication pathwith signal voltage swings different from each other.

Preferably, in the interface apparatus, the communication path is acommunication path for bidirectional parallel interface.

Preferably, in the interface apparatus, the selection information isinformation for selecting a communication mode of communication betweenthe external device.

Further, according to another aspect of the present invention, theforegoing object is attained by providing an interface apparatus fortransmitting and receiving information with an external device via acommunication path, comprising: acquisition means for acquiringselection information supplied from the external device via thecommunication path; and input means for setting a threshold value as areference value for inputting a signal on the communication path, basedon the selection information acquired by the acquisition means, andinputting information supplied from the external device via thecommunication path, with the threshold value as the reference value.

Preferably, the interface apparatus further comprises signalvoltage-swing selection means for selecting a signal voltage swing upondriving the communication path based on the selection informationacquired by the acquisition means, and the communication path is drivenwith the signal voltage swing selected by the voltage-swing selectionmeans.

Preferably, in the interface apparatus, the input means includes: aplurality of input devices, having input terminals connected to thecommunication path, and employing threshold values different from eachother; and a selection device for selectively inputting a signal on anyof output terminals of the input devices, based on the selectioninformation.

Preferably, in the interface apparatus, the selection information isinformation for selecting a communication mode of communication betweenthe external device.

Further, according to another aspect of the present invention, theforegoing object is attained by providing an interface apparatus fortransmitting and receiving information with an external device via acommunication path, comprising: acquisition means for acquiringselection information supplied from the external device via thecommunication path; drive means for selecting any of a plurality ofdrive methods based on the selection information acquired by theacquisition means, and driving the communication path; and input meansfor setting a threshold value as a reference value for inputting asignal on the communication path, based on the selection informationacquired by the acquisition means, and inputting information suppliedfrom the external device via the communication path, with the thresholdvalue as the reference value.

Preferably, in the interface apparatus, the plurality of drive methodsincludes a first drive method for driving the communication path in anopen-collector drive and a second drive method for driving thecommunication path in a totem-pole drive.

Preferably, in the interface apparatus, the plurality of drive methodsincludes a plurality of drive methods for driving the communication pathwith signal voltage swings different from each other.

Preferably, in the interface apparatus, the input means includes: aplurality of input devices, having input terminals connected to thecommunication path, and employing threshold values different from eachother; and a selection device for selectively inputting a signal on anyof output terminals of the input devices, based on the selectioninformation.

Preferably, in the interface apparatus, wherein the communication pathis a communication path for bidirectional parallel interface.

Preferably, in the interface apparatus, the selection information isinformation for selecting a communication mode of communication betweenthe external device.

Further, according to another aspect of the present invention, theforegoing object is attained by providing an interface apparatus forconnecting a plurality of devices via a communication path, comprising:selection-information supply means for supplying selection informationfrom one device to another device via the communication path; andselection means for selecting one of a plurality of drive methods fordriving the communication path from the side of the other device, basedon the selection information supplied by the selection-informationsupply means, wherein transmission and reception of information betweenthe devices is performed by driving the communication path in the drivemethod selected by the selection means.

Preferably, the interface apparatus further comprises setting means forsetting a drive method for driving the communication path incorrespondence with the selection information, on the side of the onedevice.

Preferably, in the interface apparatus, the plurality of drive methods,selectable by the selection means, includes a first drive method fordriving the communication path in an open-collector drive and a seconddrive method for driving the communication path in a totem-pole drive.

Preferably, in the interface apparatus, the plurality of drive methodsincludes a plurality of drive methods for driving the communication pathwith signal voltage swings different from each other.

Preferably, in the interface apparatus, the communication path is acommunication path for bidirectional parallel interface.

Preferably, in the interface apparatus, the selection information isinformation for selecting a communication mode of communication betweenthe external device.

Further, according to another aspect of the present invention, theforegoing object is attained by providing an interface apparatus forconnecting a plurality of devices via a communication path, comprising:selection-information supply means for supplying selection informationfrom one device to another device via the communication path; andselection means for selecting one of a plurality of threshold values asa reference value for inputting a signal on the communication path,based on the selection information supplied by the selection-informationsupply means, on the side of the other device.

Preferably, the interface apparatus further comprises setting means forsetting one of the plurality of threshold values as the reference valuefor inputting the signal on the communication path in correspondencewith the selection information, on the side of the one device.

Preferably, the interface apparatus further comprises means for drivingthe communication path with a signal voltage swing corresponding to theselection information, from the side of the one device; and means fordriving the communication path with a signal voltage swing correspondingto the selection information, from the side of the other device.

Further, according to another aspect of the present invention, theforegoing object is attained by providing an image output apparatus,comprising: an interface apparatus having the above construction; andimage formation means for forming an image based on information inputtedby the interface apparatus.

Preferably, in the image output apparatus, the image formation meansforms the image by an electrophotographic method.

Preferably, in the image output apparatus, the image formation meansforms the image in an ink-jet method.

Further, according to another aspect of the present invention, theforegoing object is attained by providing a method of negotiating fortransmitting and receiving information with an external device via acommunication path, comprising: an acquisition step of acquiringselection information supplied from the external device via thecommunication path; and a determination step of determining one of aplurality of drive methods as a drive method for driving thecommunication path, based on the selection information acquired at theacquisition step.

Further, according to another aspect of the present invention, theforegoing object is attained by providing a method of negotiating fortransmitting and receiving information with an external device via acommunication path, comprising: an acquisition step of acquiringselection information supplied from the external device via thecommunication path; and a determination step of determining a thresholdvalue as a reference value for inputting a signal on the communicationpath, based on the selection information acquired at the acquisitionstep.

Further, according to another aspect of the present invention, theforegoing object is attained by providing a method of negotiating fortransmitting and receiving information with an external device via acommunication path, comprising: an acquisition step of acquiringselection information supplied from the external device via thecommunication path; a drive-method determination step of determining oneof a plurality of drive methods as a drive method for driving thecommunication path; and a threshold-value determination step ofdetermining a threshold value as a reference value for inputting asignal on the communication path, based on the selection informationacquired at the acquisition step.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame name or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a cross-sectional view showing the structure of a laser-beamprinter as an electronic device to which a first embodiment of thepresent invention is applied;

FIG. 2 is a perspective view showing the structure of an ink-jet printeras another electronic device to which the embodiment is applied;

FIG. 3 is a block diagram showing the construction of a controller ofthe ink-jet printer in FIG. 2;

FIG. 4 is a block diagram showing the construction of a printer controlsystem according to the embodiment;

FIG. 5 is an explanatory view showing the structure of interfaceconnecting a host computer and a printer;

FIG. 6 is a timing chart showing transmission/reception (negotiation) ofcommunication-mode change information;

FIG. 7 is a flowchart showing operation of the host computer uponnotifying the communication-mode change information;

FIG. 8 is a block diagram showing the construction of an interfacecircuit on the printer side;

FIG. 9 is a logic diagram showing the construction of an output circuit;

FIG. 10 is a flowchart showing processing on the printer side uponreceiving the communication-mode change information from the hostcomputer and change the communication mode;

FIG. 11 is a flowchart showing communication-mode setting processing;

FIG. 12 is a logic diagram showing the construction of the outputcircuit corresponding to two types of signal voltage swings, accordingto a second embodiment;

FIG. 13 is a logic diagram showing the construction of an input circuitcorresponding to the two types of signal voltage swings, according tothe second embodiment;

FIG. 14 is a logic diagram showing the construction of the outputcircuit 801 according to a third embodiment;

FIG. 15 is a table showing communication modes in the output circuit inFIG. 14; and

FIG. 16 is a block diagram showing the construction of an interfacecircuit on the host computer side.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

First Embodiment

First, an example of the structure of a laser-beam printer and anink-jet printer as preferred printers to which a first embodiment of thepresent invention is applied will be described. Note that the presentembodiment is applicable to various types of printers in addition to thelaser-beam printer and ink-jet printer, and further applicable toelectronic devices other than the printers.

FIG. 1 is a cross-sectional view showing the structure of the laser-beamprinter as an electronic device to which the present embodiment isapplied. In FIG. 1, reference numeral 1500 denotes a laser-beam printer(LBP) main body which receives print information (character codes, imagedata etc.) supplied from a host computer (not shown) as a connectedexternal device, form information or macro commands, and stores thereceived information. The LBP main body 1500 generates characterpatterns or form patterns based on the stored information, and forms animage on a print sheet as a print medium.

Numeral 1501 denotes an operation panel on which operation switches andLED display devices are provided. Numeral 1000 denotes a printer controlunit which controls the overall LBP main body 1500. Also, the printercontrol unit 1000 interprets the character information and the likesupplied from the host computer. The printer control unit 1000 mainlyconverts the character information into a video signal of acorresponding character pattern or converts the image information into avideo signal, and outputs the video signal into a laser driver 1502.

The laser driver 1502, which is used for driving a semiconductor laser1503, ON/OFF controls the semiconductor laser 1503 which emits a laserbeam 1504. The laser beam 1504 is swayed by a rotating polygon mirror1505, scan-exposing on an electrostatic drum 1506. This forms anelectrostatic latent image of a character pattern on the electrostaticdrum 1506.

The latent image is developed by a development unit 1507 provided aroundthe electrostatic drum 1506 and transferred onto the print sheet. Theprint sheet is a cut sheet set in a paper cassette 1508 attached to theLBP main body 1500. The cut sheet is fed into the apparatus by apaper-feed roller 1509 and conveyance rollers 1510 and 1511, andsupplied to the electrostatic drum 1506.

FIG. 2 is a perspective view showing the structure of an ink-jetprinting apparatus (IJRA) as another electronic device to which theembodiment is applied.

In FIG. 2, numeral 5005 denotes a lead screw which rotates viadrive-force transmission gears 5009 and 5011, interlocking withforward/reverse rotation of a drive motor 5013. A carriage HC engagedwith a spiral groove 5004 of the lead screw 5005 has a pin (not shown),and it is reciprocally moved in arrows a and b directions. The carriageHC has an ink-jet cartridge IJC.

Numeral 5002 denotes a paper holding plate which presses the print sheetagainst a platen 5000 along the moving direction of the carriage HC.Photocouplers 5007 and 5008 are home-position detecting members forconfirming the existence of a lever 5006 of the carriage HC in apredetermined area and changing over the rotational direction of motor5013.

Numeral 5016 denotes a support member which supports a cap member 5022for capping the front surface of the printhead. Numeral 5015 denotes asuction member which performs suction-restoration of a printhead via acap inner opening 5023 of the cap member 5022 by sucking the inside ofthe cap member 5022. Numeral 5019 denotes a member which allows acleaning blade 5017 to move in a back-and-forth direction. A main-bodysupport plate 5018 supports the cleaning blade 5017 and the member 5019.

Numeral 5012 denotes a lever for starting the suction-restoration. Thelever 5021 moves along the movement of a cam 5020 engaged with thecarriage HC. A well-known transmission mechanism such as clutch changecontrols a drive force from the drive motor. When the carriage HC is atthe home position area, desired one of these capping, cleaning andsuction-restoration is executed at its corresponding position by thelead screw 5005. Any of these processings applicable to the printer, ifa desired processing is performed at a well-known timing.

FIG. 3 is a block diagram showing the construction of a controller ofthe ink-jet printer in FIG. 2. In FIG. 3, numeral 1700 denotes aninterface circuit for transmitting/receiving print information and othervarious information; 1701, an MPU which reads a control program in a ROM1702 and controls the ink-jet printer based on the read program; 1702,the ROM for storing control programs, host print information and thelike; 1703, a dynamic RAM (DRAM) for storing various data (printinformation, print data supplied to the printhead, and the like).

Numeral 1704 denotes a gate array which performs supply control of printdata to a printhead 1708. The gate array 1704 also performsdata-transfer control among the interface circuit 1700, the MPU 1701 andthe DRAM 1703. Numeral 1710 denotes a carrier motor for transferring theprinthead 1708; 1709, a conveyance motor for conveying the print sheet;1705, a head driver for driving the printhead 1708; 1706, a motor driverfor driving the conveyance motor 1709; and 1707, a motor driver fordriving the carrier motor 1710.

When print information is inputted via the interface circuit 1700 fromthe host computer as a connected external device, the gate array 1704converts the print information into output information for printing,under the control of the MPU 1701, and supplies the output informationto the head driver 1705. The motor drivers 1706 and 1707 are driven, andthe head driver 1705 is driven based on the output information, thusprint operation is performed.

FIG. 4 is a block diagram showing the construction of a printer controlsystem according to the embodiment. Note that FIG. 4 shows theabove-described laser-beam printer (1500) connected to the host computer(3000). Hereinbelow, a system connected to a host computer and alaser-beam printer will be described as an example of system where twoelectronic devices are connected via an interface device.

In the host computer 3000, a CPU 1 performs document processing thengenerates print information and supplies the print information to theprinter 1500, for example, while controlling the respective devicesconnected to a CPU bus 4, based on an operating system (OS), applicationprograms, a printer driver, control programs and the like, stored in aprogram ROM 3 b. Note that the control programs will be described indetail later.

Numeral 3 a denotes a font ROM in which font data and the like used indocument processing are stored; 3 c, a data ROM in which various dataused in the document processing are stored; and 2, a RAM used as a mainmemory and a work area for the CPU 1.

Numeral 5 denotes a keyboard controller (KBC) which controls key inputfrom a keyboard 9 or a pointing device (not shown); 6, a CRT controller(CRTC) which controls display by a CRT display (CRT) 10; 7, anexternal-memory controller (MC) which controls an external memory 11comprising a hard disk (HD) and a floppy disk (FD) and the like forstoring a boot program, various application programs, font data, a userfile, an editing file and the like.

Numeral 8 denotes a printer controller (PRTC) as an interface circuitfor the printer. The printer controller 8 is connected to the printer1500 via an interface cable 21 for transmitting/receiving informationwith the printer 1500. The printer controller 8 can drive signal linesincluded in the interface cable 21 by a plurality of drive methods. Forexample, the printer controller 8 can drive the control signal lines inthe open-collector drive method or the totem-pole drive method. Theprinter controller 8 can change a drive method in accordance with, e.g.,a 5 V signal voltage swing (or power voltage) or a 3.3 V signal voltageswing (or power voltage).

Note that the CPU 1 executes, e.g., development of outline font(rasterize) in a development area provided on the RAM 2, thus enablesWYSIWYG on the CRT 10. Further, the CPU 1 opens various registeredwindows based on a command designated by a mouse cursor (not shown) orthe like, and executes various data processing.

In the printer 1500, a CPU 12 controls the various devices connected toa CPU bus 15, based on the control programs and the like stored in aprogram ROM 13 b or an external memory 14. The CPU 12 outputs an imagesignal as output information to a printer engine 17 connected via aprinter interface circuit 16. Note that the control programs will bedescribed in detail later.

Numeral 13 a denotes a font ROM in which font data used upon generationof output information is stored; 13 c, a data ROM for storinginformation used on the host computer 3000; and 14, an external memorysuch as a hard disk, also for storing information used on the hostcomputer 3000.

The CPU 12, which is capable of processing of communication with thehost computer 3000 via the interface circuit 18, can notify informationin the printer 1500 to the host computer 3000. The interface circuit 18can drive the interface cable 21 in a plurality of drive methods. Forexample, the interface circuit 18 drives the interface cable 21 by theopen-collector drive method or the totem-pole drive method. Theinterface circuit 18 can change the drive method in accordance with,e.g., a 5 V signal voltage swing (or power voltage) or a 3.3 V signalvoltage swing (or power voltage).

Numeral 19 denotes a RAM used as a main memory or a work memory for theCPU 12. The capacity of the RAM 19 can be expanded by connectingoptional RAM(s) to memory-expansion port(s) (not shown). Note that theRAM 19 is used as an output-information development area, anenvironmental-data storage area, a non-volatile RAM (NVRAM) and thelike. The above-described external memory 14 comprising a hard disk(HD), an IC card and the like is controlled by an external memorycontroller (MC) 20. The external memory 14 is connected as an optionalmemory, and used for storing font data, emulation programs, form dataand the like.

Numeral 1501 denotes the above-described operation panel on whichoperation switches and LED display devices are provided.

FIG. 5 is an explanatory view showing the structure of interfaceconnecting a host computer and a printer. FIG. 5 shows various signalsin an 8-bit width parallel interface generally used as a printerinterface.

In this example, data is sent via bidirectional signal lines (Data 1 toData 8) 502. Signal lines 501 and 503 to 505 are control signal linescontrolled by the host computer 3000. Signal lines 506 to 510 arecontrol signal lines controlled by the printer 1500.

In this embodiment, the host computer 3000 notifies the printer 1500 ofcommunication-mode change information to instruct to changecommunication mode (open-collector, totem-pole and the like) bycontrolling the signal lines 501 and 503 to 510 to set signal values(logic levels) of signals on these signal lines into a specificcombination, and setting of the interface circuit 18 of the printer 1500is made based on the information. For example, if a communication modewhere signal lines are driven in the totem-pole drive method isselected, the host computer 3000 may notify the printer 1500 ofcommunication-mode change information designating the drive method. Notethat in the following example, the host computer side notifies theprinter side of communication-mode change information to control acommunication mode of the printer side. However, it may be arranged suchthat the printer side notifies the host computer side ofcommunication-mode change information to control a communication mode ofthe host computer side. It is more preferable that communication-modechange can be instructed from both sides.

FIG. 6 is a timing chart showing the transmission/reception(negotiation) of communication-mode change information. FIG. 7 is aflowchart showing operation of the host computer 3000 upon notifying thecommunication-mode change information. Hereinbelow, operation of theprinter controller 8 as an interface circuit of the host computer 3000side will be described with reference to FIGS. 6 and 7. Note that inthis embodiment, the printer controller 8 operates under the control ofthe CPU 1 based on the control program in the program ROM 3 b.

First, at step S701, communication-mode change information is obtained.This information may be defined as “0001(hex)” when the signal lines 501to 510 are used in the open-collector drive, while “0002(hex)” when thesignal lines 501 to 510 are used in the totem-pole drive. Further, thecommunication-mode change information may be inputted from the keyboard9 or the like, or may be read from the data ROM 3 c or the like.Otherwise, any other method can be used to obtain the communication-modechange information. The control program may be automatically startedwhen the host computer 3000 is turned on, or when it is detected thatthe printer 1500 has been turned on.

At step S702, the obtained communication-mode change information isoutputted onto a signal line Data (502) (Event 0). At step S703, asignal line nSelectIn (505) is turned to H (high) level, while a signalline nAutoFd (503) is turned to L (low) level (Event 1). This causes theprinter 1500 to recognize a communication-mode change request.

At step S704, it is determined whether or not the communication-modechange request has been recognized. This determination is made based onwhether or not a signal line PError (508) is at the H level, whether ornot a signal line nAck (506) is at the L level, whether or not a signalline nFault (510) is at the H level, and whether or not a signal lineSelect (509) is at the H level (Event 2). Hereinafter, this status wherethe signal lines are at the above levels will be referred to as a“request-recognized status”.

If it is determined that the printer 1500 has become into therequest-recognized status within a predetermined period, the processproceeds to step S705, at which a signal line Strobe (501) is set to theL level (Event 3) so that the printer 1500 can input thecommunication-mode change information, and the signal line Strobe (501)and a signal line nAutoFd (503) are set to the H level (Event 4).

On the other hand, if it is determined at step S704 that the printer1500 has not become into the request-recognized status within thepredetermined period, a signal line nSelectIn (505) is set to the Llevel and the signal line nAutoFd (503) is set to the H level at stepS707.

At step S706, to recognize the completion of communication-mode change(Event 5) and the completion of processing related to thecommunication-mode change, it is waited until the level of the signalline nAck (506) becomes the H level (Event 6). Hereinafter,communication in the set communication mode is possible.

Note that on the host computer 3000 side, a communication mode of theprinter controller 8 is set to a mode corresponding to the abovecommunication-mode change information. This setting is made before thecompletion of processing as shown in FIG. 7, i.e., before starting ofcommunication in the set communication mode.

FIG. 8 is a block diagram showing the construction of the interfacecircuit 18 of the printer 1500. A controller 803 generates signalsperror, nack, busy, select, datao as internal signals corresponding tosignals to be outputted onto the signal lines PError (508), nAck (506),Busy (507), nFault (510), Select (509) and Data (502). Further, thecontroller 803 inputs a signal datai corresponding to a signal inputtedvia the signal line Data (502), and signals nstrobe, nautofd, ninit,nselectin corresponding to the signal lines nStrobe (501), nAutoFd(503), nInit (504) and nSelectIn (505). The controller 803 it performscommunication-mode change under the control of the CPU 12, as well asother general host-computer functions.

Output circuits 801 a to 801 f respectively output signals correspondingto logical levels of the signals perror, nack, busy, select and dataoonto the signal lines PError (508), nAck (506), Busy (507), nFault(510), Select (509) and Data (502). Note that the output circuit 801 ato 801 e have the same construction. The output circuit 801 f compriseseight output circuit 801 (each corresponding to a bit of Data (502)). Inthe interface cable 21, a drive method (e.g., open-collector ortotem-pole) of the signal lines is set by a control signal DRVSEL.

Input circuits 802 a and 802 b input signals through the signal linesData (502), nStrobe (501), nAutoFd (503), nInit (504) and nSelectIn(505). The input circuit 802 a comprises eight input circuit 802; andthe input circuit 802 b, four input circuit 802.

FIG. 9 is a logic diagram showing an example of construction of theoutput circuit 801. The output circuit 801 inputs the control signalDRVSEL and internal signals such as perror. The output circuit 801generates an output signal to drive the signal lines of the interfacecable 21 such as PError.

In FIG. 9, numeral 901 denotes an inverter; 902, an OR gate; 903, an ANDgate; and 904, a 3-state buffer. Note that as manufacturing process ofthese gates, a bipoler process or a CMOS process may be employed.However, any other processes may be used for manufacturing the gates. Inthis embodiment, as a driving method, open-collector or totem-pole driveis used for the convenience of description. However, this does notlimits the present invention to the bipolar process, but anyconstruction substantially similar to the present construction (e.g.,open drain or CMOS output) in the CMOS process may be included.

First, the operation when the control signal DRVSEL is at the L levelwill be described. In this case, the output from the AND gate 903 isfixed to the L level. The logic levels of the internal signals (e.g.,perror) are inverted by the inverter 901, and inputted via the OR gate902 to an enable terminal of the 3-state buffer 904. That is, when theinternal signals are at the L level, the output from the 3-state buffer904 is at the L level; on the other hand, when the internal signals areat the H level, the output from the 3-state buffer 904 is at thehigh-impedance status which equals open-collector output.

Next, the operation when the control signal DRVSEL is at the H levelwill be described. In this case, the output from the OR gate 902 isfixed to the H level, and the output from the 3-state buffer 904 is inenable status. That is, the output from the 3-state buffer 904 is at thesame level of the logic levels of the internal signals, which equalstotem-pole output.

FIG. 10 is a flowchart showing the processing of obtainingcommunication-mode change information from the host computer and changea communication mode. Note that in the present embodiment, the interfacecircuit 18 operates under the control of the CPU 12 based on the controlprogram in the program ROM 13 b. This processing is started immediatelyafter the printer 1500 has been turned on.

At step S1001, the printer 1500 initializes a communication mode to theopen-collector drive by setting the control signal DRVSEL to the Llevel. Note that the initialization may be performed by means ofhardware immediately after the printer has been reset.

At step S1002, it is determined whether or not the signal line nSelectIn(505) is at the H level and the signal line nAutoFd (503) is at the Llevel, i.e., the host computer 3000 is requiring communication-modechange. If NO, the process proceeds to step S1004, at whichcommunication is performed in the communication mode set through theinitialization at step S1004. Then, after a predetermined period haselapsed, for example, the process returns to step S1002, at which theabove determination is performed. If it is determined at step S1002 thatthe communication-mode change request has been recognized(request-recognized status in Event 1), the process proceeds to stepS1003 at which communication-mode setting processing is performed. Afterthe completion of the communication-mode setting processing,communication is performed in the set communication mode.

According to the above flowchart, it is not assumed that thecommunication-mode changing request is received after settingcommunication mode has been set, however, the present embodiment isapplicable to a case where re-setting of communication mode is possible.In this case, the communication mode can be reset by periodicallyperforming step S1002 or generating interruption (“interruption” in FIG.10) when it is detected that the condition of determination at stepS1002 is satisfied. In a case where the power of the host computer 3000is turned off, if communication-mode change information instructing toset the communication mode to the open-collector drive is received, forexample, the communication mode can be changed based on the receivedinformation. This prevents overcurrent as described above.

FIG. 11 is a flowchart showing communication-mode setting processing. Atstep S1101, to notify the host computer 3000 that the communication-modechanging request has been recognized, the signal line PError (508) isset to the H level; the signal line nAck (506), to the L level; thesignal line nFault (510), to the H level; and the signal line Select(509), to the H level (Event 2).

At step S1102, communication-mode change information on the signal lineData (502) is inputted based on instruction to input thecommunication-mode change information (Events 3 and 4). At step S1103,the control signal DRVSEL is set based on the input communication-modechange information. For example, if the communication-mode changeinformation instructs to set the communication mode to the totem-poledrive, the control signal DRVSEL is set to the H level. In a case wherethe power of the host computer 3000 is turned off, if communication-modechange information instructs to set the communication mode to theopen-collector drive, the control signal DRVSEL is set to the L level.Note that in this embodiment, two drive methods are considered ascommunication modes, however, the embodiment is applicable to a caseusing three or more drive methods.

At step S1104, the signal lines PError (508), Busy (507) and Select(509) are set to normal status (Event 5). At step S1105, to notify thehost computer 3000 that the communication-mode change has beencompleted, the signal line nAck (506) is set to the H level (Event 6).

Note that in this embodiment, communication mode is changed inaccordance with communication-mode change information supplied from thehost computer 3000, however, the present embodiment is not limited tothis arrangement. For example, the embodiment is applicable to a casewhere the communication mode is changed based on an instruction from theoperation panel 1501.

FIG. 16 is a block diagram showing the construction of the printercontroller 8 of the host computer 3000. A controller 804 inputs signalson the signal lines PError (508), nAck (506), busy (507), nFault (510),Select (509) and Data (502) as signals perror′, nack′, busy′, select′and datai′. The controller 804 generates signals datao to be outputtedonto the signal line Data (502) and internal signals nstrobe′, nautofd′,ninit′ and nselectin′ corresponding to signals to be outputted onto thesignal lines nStrobe (501), nAutoFd (503), nInit (504) and nSelectIn(505). Further, the controller 804 performs communication-mode changeunder the control of the CPU 1, as well as other general printerfunctions.

After the processing as shown in FIG. 10 has been completed, thecommunication-mode change is performed before communication is startedin the new communication mode. Further, similar to the case of theinterface circuit 18, the communication-mode change can be performed bycontrolling the logic level of the control signal DRVSEL to becorresponding to communication mode (communication-mode changeinformation).

Note that the input circuits 802 c to 802 h have the same constructionas that of the input circuit 802 (see FIG. 13). The output circuit 801 gcomprises eight output circuit 801; the output circuit 801 h, fouroutput circuit 801.

The operation of the output circuit 801 and that of the input circuit802 are as described above.

According to the present embodiment, the drive method of the interfacecircuit can be appropriately changed in accordance with thespecification of a host computer of communication-destination party,which effectively utilizes the performance of a host computer (externaldevice) to be connected.

For example, if the host computer has only an open-collector typeinterface circuit, an interface circuit of the printer can be set to theopen-collector drive.

Further, if the host computer has a totem-pole type interface circuit,the interface circuit of the printer can be set to the totem-pole drive,which increases communication speed.

In a case where the power of one device which has an open-collector typeinterface circuit is turned off, overcurrent which may be by caused bythe totem-pole drive of another device can be prevented by changing thedrive method of both interface circuits to the open-collector drive.

Second Embodiment

Next, a second embodiment will be described. In this embodiment, thesignal voltage swing of an interface circuit of one device is changed,in accordance with a signal voltage swing of an interface circuit of theother device connected to the former device.

In this example, an interface circuit communicable with an interfacecircuit having a 5 V signal voltage swing and an interface circuithaving a 3.3 V signal voltage swing will be described.

FIG. 12 is a logic diagram showing the construction of an output circuitcorresponding to two types of signal voltage swings, according to thesecond embodiment. Note that the control signal DRVSEL, the internalsignal, and the output signal substantially correspond to the signals inFIG. 9. However, in this embodiment, the control signal DRVSEL functionsas a signal to change the signal voltage swing of the output signal.

In FIG. 12, numeral 1201 denotes an inverter; 1202, a 3-state bufferhaving a 3.3 V signal voltage swing; and 1203, a 3-state buffer having a5 V signal voltage swing.

When the control signal DRVSEL is at the L level, the 3-state buffer1203 is enabled. The output from the 3-state buffer 1202 becomes intohigh-impedance status, then a 5 V signal voltage swing signal isoutputted. On the other hand, when the control signal DRVSEL is at the Hlevel, the 3-state buffer 1202 is enabled. The output from the 3-statebuffer 1203 becomes into high-impedance status, then a 3.3 V signalvoltage swing signal is outputted.

Note that the control signal DRVSEL is controlled in substantially thesame manner as that in the first embodiment.

FIG. 13 is a logic diagram showing the construction of the input circuitcorresponding to two types of signal voltage swings. In FIG. 13, theinput circuit 802 inputs a signal on the signal line (e.g., nStrobe(501)) of the interface cable 21, and supplies the signal to thecontroller 803.

In FIG. 13, numeral 1301 denotes an inverter having a threshold valuecorresponding to the 3.3 V signal voltage swing; 1302, an inverterhaving a threshold value corresponding to the 5 V signal voltage swing;and 1303, a selector which selects the output from the inverter 1302when the control signal DRVSEL is at the L level, while selects theoutput from the inverter 1301 when the control signal DRVSEL is at the Hlevel.

In this construction, when the input signal (e.g., a signal on thesignal line nStrobe) has the 5 V signal voltage swing, the controlsignal DRVSEL is set to the L level, so that the input signal istransferred to the controller 803 with a threshold of about 2.5 V. Onthe other hand, when the input signal has the 3.3 V signal voltageswing, the control signal DRVSEL is set to the H level, so that theinput signal is transferred to the controller 803 with a threshold valueof about 1.6 V. Accordingly, the change of input signal can berecognized with an appropriate threshold value corresponding to a signalvoltage swing, and the signal value can be inputted. This increasescommunication speed.

Note that it is preferable to comprise both of the output circuit inFIG. 12 and the input circuit in FIG. 13, however, it is possible to useonly one of these circuits.

Third Embodiment

Next, a third embodiment will be described as a combination of the firstand second embodiment, where the open-collector drive or the totem-poledrive can be selected as a drive method of signal lines of the interfacecircuit. Also, the 5 V signal voltage swing and the 3.3 V signal voltageswing can be selected.

FIG. 14 is a logic diagram showing the construction of the outputcircuit 801 according to the third embodiment. In FIG. 14, numeral 1401and 1408 denote inverters; 1402, 1405 to 1406 and 1410, AND gates; 1403and 1407, OR gates; 1404, a 3-state buffer having a 5 V signal voltageswing; and 1409, a 3-state buffer having a 3.3 V signal voltage swing.

The control signal DRVSEL <1:0> is controlled by the controller 803 asthe control signal DRVSEL of the above embodiments. The internal andoutput signals are used as follows.

FIG. 15 is a table showing communication modes in the output circuit inFIG. 14. As shown in FIG. 15, four communication modes can be selectedas signal-line drive methods. For example, when the value of the DRVSEL<1:0> is “00”, a communication mode where the output circuit 801 in FIG.14 operates in the open-collector drive method with a 5 V signal voltageswing is selected.

In the present embodiment, the communication mode of the printer side ischanged, however, the present invention is also applicable to a casewhere the communication mode of the host computer side is changed.

Further, the present invention is applicable to, as well as a printer ora host computer, communication devices or various electronic devicesincluding the communication devices.

In the above embodiments, the open-collector and totem-pole drivemethods using the 5 V and 3.3 V signal voltage swings are described asselectable communication modes, however, the present invention is notlimited to these communication modes, but applicable to any methodregarding connection between interface circuits.

Further, in the above embodiments, the interface circuits are controlledby means of software, however, the control can be made by means ofhardware such as logic circuits.

APPLICATION EXAMPLE

Next, an example where the first to third embodiments are applied tocommunication based on a communication protocol defined in the IEEEstandard 1284-1994 will be described. In this communication protocol, acompatibility mode, a Nibble mode, an ECP mode and the like areavailable. These communication modes are described in “StandardSignaling Method for a Bi-Directional Parallel-Peripheral Interface forPersonal Computers: IEEE P1284 D2.00 Sep. 10, 1993”.

In this example, when the compatibility mode is selected, theopen-collector drive is selected as a drive method, and when the Nibblemode or the ECP mode is selected, the totem-pole drive is selected asthe drive method. The selection is realized by transmittingcommunication-mode change information from the host computer 3000 to theprinter 1500 in the negotiation as shown in FIG. 6.

First, the operation of the host computer side will be described withreference to FIG. 7. Immediately after the start-up, the communicationmode is set to the compatibility mode. At step S701, communication-modechange information corresponding to another communication mode to be set(e.g., compatibility mode) is obtained. At step S702, the obtainedcommunication-mode change information is outputted onto the signal lineData (502) (Event 0).

At step S703, the signal line nSelectIn (505) is set to the H level, andthe signal line nAutoFd (503) is set to the L level. This causes theprinter 1500 to recognize communication-mode change (negotiation). Notethat in the above communication protocol, when the signal line nSelectIn(505) is at the L level, the compatibility mode is selected as thecommunication mode, and the transition from the L level to the H levelindicates communication-mode change from the compatibility mode toanother mode (Nibble mode, ECP mode and the like). Note that thecommunication-mode change is completed upon the completion ofnegotiation.

The operation at steps subsequent to step S703 is as described in thefirst to third embodiments.

In the present example, the output of communication-mode changeinformation to the printer 1500 is instruction to change communicationmode as a drive method (e.g., open-collector drive method), and it isalso instruction to change communication mode as a communicationprotocol (e.g., compatibility mode).

Next, the operation of the printer side will be described with referenceto FIG. 10. As the power is turned on at step S1001, the printer 1500recognizes that the signal line nSelectIn (505) is at the L level (incompatibility mode), and initializes the drive method to open-collectordrive by setting the control signal DRVSEL to the L level. Note thatwhen the host computer 3000 normally operates or when the power is notturned on, negotiation between the host computer and the printer has notbeen made at step S1001, therefore the signal line nSelectIn (505) is atthe L level.

At step S1003, communication-mode setting is performed. Specifically, acommunication mode (e.g., totem-pole drive) as a drive method and acommunication mode (e.g., ECP mode) as a communication protocol are setbased on the communication-mode change information.

Note that the operation at steps S1002 and that at S1004 are the same asthose in the first to third embodiments.

As described above, in this example, based on the instruction from thehost computer 3000, when a communication mode as a communicationprotocol is changed, a communication mode as a drive method is alsochanged. That is, when the compatibility mode is changed to anothermode, the drive method is changed from open-collector drive tototem-pole drive.

According to this example, in a case where compatibility mode is set bythe host computer, the drive method of an interface circuit is set tothe open-collector drive, and in a case where another communication modeis set, the drive method of the interface circuit is set to thetotem-pole drive. This enables high-speed communication in any ofcommunication modes except the compatibility mode while maintainingcompatibility of the compatibility mode.

Further, conventionally, in a case where the power of the host computeris turned off and the power of the printer is turned on, some hostcomputer fail to normally turn on their power, since a limiter operatesdue to occurrence of overcurrent at their interface circuit. However,according to the present example, since the signal line nSelectIn is atthe L level when the power of the host computer is turned off, it isconsidered that the printer is in the compatibility mode, and theinterface circuit of the printer is forcibly set to the open-collectordrive. Accordingly, overcurrent at the interface circuit of the hostcomputer can be prevented, thus the power of the host computer can benormally turned on.

Other Embodiment

The present invention can be applied to a system constituted by aplurality of devices (e.g., host computer, interface, reader, printer)or to an apparatus comprising a single device (e.g., copy machine,facsimile).

Further, the object of the present invention can be also achieved byproviding a storage medium storing program codes for performing theaforesaid processes to a system or an apparatus, reading the programcodes with a computer (e.g., CPU, MPU) of the system or apparatus fromthe storage medium, then executing the program.

In this case, the program codes read from the storage medium realize thefunctions according to the embodiments, and the storage medium storingthe program codes constitutes the invention.

Further, the storage medium, such as a floppy disk, a hard disk, anoptical disk, a magneto-optical disk, CD-ROM, CD-R, a magnetic tape, anon-volatile type memory card, and ROM can be used for providing theprogram codes.

Furthermore, besides aforesaid functions according to the aboveembodiments are realized by executing the program codes which are readby a computer, the present invention includes a case where an OS(operating system) or the like working on the computer performs a partor entire processes in accordance with designations of the program codesand realizes functions according to the above embodiments.

Furthermore, the present invention also includes a case where, after theprogram codes read from the storage medium are written in a functionexpansion card which is inserted into the computer or in a memoryprovided in a function expansion unit which is connected to thecomputer, CPU or the like contained in the function expansion card orunit performs a part or entire process in accordance with designationsof the program codes and realizes functions of the above embodiments.

As described above, the present invention provides an electronic devicewhich can be appropriately connected to external devices having variousspecifications.

The present invention is not limited to the above embodiments andvarious changes and modifications can be made within the spirit andscope of the present invention. Therefore, to appraise the public of thescope of the present invention, the following claims are made.

What is claimed is:
 1. An apparatus for communicating with an externaldevice via a communication interface, the apparatus having a pluralityof communication modes in which transmission rate capabilities aredifferent from each other, said apparatus comprising: an acquisitionunit, arranged to acquire a communication mode change request from theexternal device via the communication interface; a plurality of drivecircuits; and a setting unit, arranged to set one of the plurality ofcommunication modes by selecting one of said plurality of drive circuitsbased on the communication mode change request acquired by saidacquisition unit, wherein the selected drive circuit electrically drivesa communication signal line of the communication interface.
 2. Theapparatus according to claim 1, wherein said plurality of drive circuitsinclude a first drive circuit adapted to drive the communication signalline in an open-collector drive manner and a second drive circuitadapted to drive the communication signal line in a totem-pole drivemanner.
 3. The apparatus according to claim 1, wherein said plurality ofdrive circuits drive the communication signal line with signal voltageswings different from each other.
 4. The apparatus according to claim 1,wherein the communication interface includes a bidirectional parallelinterface.
 5. The apparatus according to claim 1, wherein the externaldevice comprises a host computer.
 6. The apparatus according to claim 1,further comprising an image former, arranged to form an image based oninformation inputted from the external device via the communicationinterface.
 7. The apparatus according to claim 6, wherein said imageformer forms the image by an electrophotographic method.
 8. Theapparatus according to claim 6, wherein said image former forms theimage by an ink-jet method.
 9. A system comprising a plurality ofdevices connected with each other via a communication interface, whereina first device of said plurality of devices comprises aselection-information supplier, arranged to supply selection informationvia the communication interface, and wherein a second device of saidplurality of devices comprises a signal line driver unit, arranged toselect one of a plurality of drive methods based on the selectioninformation supplied by the selection information supplier, and furtherarranged to electrically drive at least one communication signal line ofthe communication interface according to the selected drive method. 10.The system according to claim 9, wherein the second device furthercomprises a setter, arranged to set an input method for capturing asignal on the at least one communication signal line in correspondencewith the selected drive method.
 11. The system according to claim 9,wherein the plurality of drive methods, selectable by the signal linedriver unit, includes a first drive method for electrically driving theat least one communication signal line in an open-collector drive mannerand a second drive method for electrically driving the at least onecommunication signal line in a totem-pole drive manner.
 12. The systemaccording to claim 9, wherein the plurality of drive methods includes adrive method for electrically driving the at least one communicationsignal line with signal voltage swings different from each other. 13.The system according to claim 9, wherein the communication interfaceincludes a communication path for a bidirectional parallel interface.14. The system according to claim 9, wherein the selection informationis information for selecting a communication mode for communicatingbetween said plurality of devices.
 15. A method of negotiating forcommunication with an external device via a communication interface, thecommunication being performed under one of a plurality of communicationmodes in which transmission rate capabilities are different from eachother, said method comprising: an acquisition step of acquiring acommunication mode change request from the external device via thecommunication interface; and a drive step of setting one of theplurality of communication modes by selecting one of a plurality ofdrive circuits based on the communication mode change request acquiredin said acquisition step and electrically driving a communication signalline of the communication interface by the selected drive circuit. 16.The method according to claim 15, wherein the plurality of drive methodsincludes a first drive method for driving the at least one communicationline in an open-collector drive manner and a second drive method fordriving the at least one communication line in a totem-pole drivemanner.
 17. The method according to claim 15, wherein the plurality ofdrive methods includes a plurality of drive methods for driving the atleast one communication line with signal voltage swings different fromeach other.
 18. The method according to claim 15, wherein thecommunication interface includes a communication path for abidirectional parallel interface.
 19. The method according to claim 15,wherein the selection information is information for selecting acommunication mode for communicating with the external device.
 20. Anapparatus for performing communication in accordance with IEEE Standard1284, said apparatus comprising: a signal line driver unit, arranged toelectrically drive a communication signal line; and an outputcontroller, arranged to cause said signal line driver unit to drive thecommunication signal line by a first drive method when a compatibilitymode is set as a communication mode, and to cause said signal linedriver unit to drive the communication signal line by a second drivemethod different from the first drive method when a Nibble mode or anECP mode is set as the communication mode.
 21. The apparatus accordingto claim 20, wherein the first drive method is an open-collector drivemethod, and the second drive method is a totem-pole drive method. 22.The apparatus according to claim 20, wherein the first and second drivemethods are drive methods for driving the communication line with signalvoltage swings that are different from each other.
 23. The apparatusaccording to claim 20, further comprising: an input unit, arranged tocapture a signal on the communication line; and an input controller,arranged to cause said input unit to capture the signal on thecommunication line by a first input method when the compatibility modeis set as the communication mode, and to cause said input unit tocapture the signal on the communication line by a second input methoddifferent from the first input method when the Nibble mode or the ECPmode is set as the communication mode.
 24. The apparatus according toclaim 23, wherein said input unit includes: a plurality of inputdevices, including input terminals connected to the communication line,and employing reference values different from each other; and aselection device for selectively outputting from one of the plurality ofinput devices based on the communication mode.
 25. The apparatusaccording to claim 20, further comprising a transmitter, arranged totransmit print information to a printer via the communication line inaccordance with IEEE Standard
 1284. 26. The apparatus according to claim20, further comprising: a receiver, arranged to receive printinformation via the communication line in accordance with the IEEEStandard 1284; and an image former, arranged to form an image based onthe received print information.
 27. The apparatus according to claim 26,wherein said image former forms the image by an electrophotographicmethod.
 28. The apparatus according to claim 26, wherein said imageformer forms the image using an ink-jet method.
 29. The apparatusaccording to claim 20, wherein said signal line driver unit includes: a3-state buffer; and a logic circuit, arranged to input an internalsignal, indicating a same logic level as an output signal to beoutputted from the 3-state buffer, and a signal corresponding to thecommunication mode, and to generate an output signal to be supplied toan input terminal of the 3-state buffer and a control signal to besupplied to an enable terminal of the 3-state buffer, and wherein thefirst drive method is an open-collector drive method, and the seconddrive method is a totem-pole drive method.
 30. An apparatus forperforming communication in accordance with IEEE Standard 1284,comprising: an input unit, arranged to capture a signal on acommunication line; and an input controller, arranged to cause saidinput unit to capture the signal on the communication line by a firstinput method when the compatibility mode is set as a communication mode,and to cause said input unit to capture the signal on the communicationline by a second input method different from the first input method whena Nibble mode or an ECP mode is set as the communication mode.
 31. Theapparatus according to claim 30, wherein said input unit includes: aplurality of input devices, including input terminals connected to thecommunication line, and employing reference values different from eachother; and a selection device for selectively outputting from one of theplurality of input devices based on the communication mode.
 32. Theapparatus according to claim 30, further comprising a transmitter,arranged to transmit print information to a printer via thecommunication line in accordance with the IEEE Standard
 1284. 33. Theapparatus according to claim 30, further comprising: a receiver,arranged to receive print information via the communication line inaccordance with the IEEE Standard 1284; and an image former, arranged toform an image based on the received print information.
 34. The apparatusaccording to claim 33, wherein said image former forms the image by anelectrophotographic method or an ink-jet method.
 35. A method ofperforming communication in accordance with IEEE Standard 1284,comprising: a drive step of electrically driving a communication signalline with a drive unit; and an output control step of causing the driveunit to electrically drive the communication signal line by a firstdrive method when a compatibility mode is set as a communication mode,and causing the drive unit to drive the communication line by a seconddrive method different from the first drive method when a Nibble mode oran ECP mode is set as the communication mode.
 36. The method accordingto claim 35, wherein the first drive method is an open-collector drivemethod, and the second drive method is a totem-pole drive method. 37.The method according to claim 36, wherein the drive unit includes: a3-state buffer; and a logic circuit, arranged to input an internalsignal, indicating a same logic level as an output signal to beoutputted from the 3-state buffer, and a signal corresponding to thecommunication mode, and to generate an output signal to be supplied toan input terminal of the 3-state buffer and a control signal to besupplied to an enable terminal of the 3-state buffer.
 38. The methodaccording to claim 35, wherein the first and second drive methods aredrive methods for driving the communication signal line with signalvoltage swings different from each other.
 39. The method according toclaim 35, further comprising: an input step of capturing a signal on thecommunication line with an input unit; and an input control step ofcausing said input step to capture the signal on the communicationsignal line with a first input method when the compatibility mode is setas the communication mode, and causing said input step to capture thesignal on the communication line by a second input method different fromthe first input method when the Nibble mode or the ECP mode is set asthe communication mode.
 40. The method according to claim 39, whereinthe input unit includes: a plurality of input devices, including inputterminals connected to the communication line, and employing referencevalues different from each other; and a selection device for selectivelyoutputting from one of the plurality of input devices, based on thecommunication mode.
 41. The method according to claim 35, furthercomprising a transmission step of transmitting print information to aprinter via the communication signal line in accordance with the IEEEStandard
 1284. 42. The method according to claim 35, further comprising:a reception step of receiving print information via the communicationsignal line in accordance with IEEE Standard 1284; and an imageformation step of forming an image based on the received printinformation.
 43. The method according to claim 42, wherein, in saidimage formation step, the image is formed by an electrophotographicmethod.
 44. The method according to claim 42, wherein, in said imageformation step, the image is formed by an ink-jet method.
 45. A methodof performing communication in accordance with IEEE Standard 1284,comprising: an input step of capturing a signal on a communication lineby an input unit; and an input control step of causing said input stepto capture the signal on the communication line by a first input methodwhen the compatibility mode is set as the communication mode, andcausing said input step to capture the signal on the communication lineby a second input method different from the first input method when theNibble mode or the ECP mode is set as the communication mode.
 46. Themethod according to claim 45, wherein the input unit includes: aplurality of input devices, including input terminals connected to thecommunication line, and employing reference values different from eachother; and a selection device for selectively outputting from one of theplurality of input devices, based on the communication mode.
 47. Themethod according to claim 45, further comprising a transmission step oftransmitting print information to a printer via the communication linein accordance with the IEEE Standard
 1284. 48. The method according toclaim 45, further comprising: a reception step of receiving printinformation via the communication line in accordance with the IEEEStandard 1284; and an image formation step of forming an image based onthe received print information.
 49. The method according to claim 48,wherein, in said image formation step, the image is formed by anelectrophotographic method or an ink-jet method.